/Engine/Plugins/Experimental/ModularGameplay/Source/ModularGameplay/Public/Components/GameFrameworkComponentManager.h
The extension system allows registering for arbitrary event callbacks on receiver actors. These are the default events but games can define, send, and listen for their own. AddReceiver was called for a registered class and components were added, called early in initialization
static [FName](API\Runtime\Core\UObject\FName) NAME_ReceiverAdded = FName("ReceiverAdded");